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Grading the Special Illustration Rare Cornerstone Mask Ogerpon ex from Twilight Masquerade isn't worth it at current prices. At $10.96 raw against $90.72 for a PSA 10, that works out to -10% ROG. Grading and shipping fees would eat whatever margin is there.
Most grading maths asks you to guess your odds of a PSA 10 first. This works backwards from the prices instead and tells you what those odds would have to be.
The number is different on every card. It's how confident you'd need to be that this copy gems before grading pays for itself, so 20% means roughly a 1 in 5 shot and 50% means a coin flip.
Grade it if you rate your copy better than that, leave it raw if you don't.
It assumes a 9 is the worst you'll get. Centering and edge whitening send plenty of modern cards back at 8 or lower, and that's not priced in here, so treat this as the floor of the bar rather than the whole of it. Selling fees aren't counted either.
(cost - PSA 9) ÷ (PSA 10 - PSA 9)
Not worth grading at any odds
Even a guaranteed PSA 10 ($90.72) wouldn't cover your $100.96 cost (raw + grading + shipping).
A clean raw copy is worth more to you than a slabbed one here. Sell it as is, or keep it for the collection.
Among the 92 cards in Twilight Masquerade with PSA 10 sale data, Cornerstone Mask Ogerpon ex ranks 26th for Return on Grading and 27th by PSA 10 price. Of the 11 Special Illustration Rare cards with PSA 10 sales, it is 6th for Return on Grading. The median PSA 10 in this set sells for $57.14. 4 of the 92 clear a 100% Return on Grading.
